The invention relates to a filter element for end face inflow, comprising alternating flat layers and folded layers which form channels having a triangular cross section, in which the channels are alternately sealed at one end or the other so that the fluid to be filtered must flow through the filter medium. The invention further relates to a filter in which the described filter element is installed.
Filter elements with end face inlets are already known in the art. These filters are wound, for example, from filter layers that are alternately flat and wavy. This creates channels, the alternating seal of which forces the fluid to flow through the filter medium. Accordingly, the medium to be filtered enters through the channels which are open on the end face at the inlet side. Within the filter element, the medium switches to channels that are adjacent to the inlet channels and are open on the discharge side. This causes the fluid to be filtered.
The aim of such a filter configuration on the one hand is to minimize the volume required for the filter element. The end faces of the filter element form an inlet side and a discharge side, respectively. The channels that communicate with the inlet side form the unfiltered side of the filter, while the discharge-side channels form the filtered side. As a result, these filters are very compact and can be installed, for instance, as inline filters in pipes. At the same time, the aim is to increase the filter capacity as far as possible. However, with a wavy configuration of the filter layer this is possible only to a limited extent. It has been shown that in the inlet channels there is little flow in the contact area between the wavy filter layer and the flat filter layer, so that fewer particles are deposited on the filter medium in these areas than in others. Due to the irregular loading of the filter medium, the filter reaches the end of its service life, which is determined by the pressure drop across the filter, at a time when parts of the filter medium have not yet reached their loading limit.
It is also known in the art, for example from WO 87/01301 and U.S. Pat. No. 3,020,977, to use zigzag-folded or pleated filter layers in wound filters. They are intended as spacer layers between the individual filter layers. For this purpose, a filter layer involved in the filtering of the fluid is alternately wound with an additional layer. The additional layer is used, for example, for electrostatically discharging the fluid to be filtered or the particles contained therein (WO 87/01301). The flat layer can furthermore be used to obtain a reliable spacing of the folded layers involved in the filtering (U.S. Pat. No. 3,020,977). For this purpose, the flat layer is introduced into the filter as an additional layer and thus divides the rhombic channels created by the zigzag-folded filter layers in one of the diagonals.
Such filters are expensive to produce, however. Furthermore, only half of the layers are involved in filtering the fluid. As a result, the volume to filter area ratio is not optimized.